Lice

INSECTA PARASITES

Phthiraptera Introduction

Arthropod Classification - copyright nabrown RVC

Lice are obligate ectoparasites of every avian and most mammalian species. They are only a few milimetres long and like fleas, are wingless but unlike fleas are dorsoventally flattened.

Lice are host specific, permanent parasites which cause pediculosis. The louse saliva and faeces contains allergenic substances which causes irritation, rubbing, licking and skin damage to the host which will decrease the host's productivity.

Mammalian lice species have a single pair of claws on the ends of stout legs, whereas avian lice species have a double claw on each leg.

There are two main groups of veterinary importance, the mallophaga (chewing lice) and anoplura (sucking lice).

Mallophaga

Also known as chewing lice or biting lice

• Broad head

• Thorax narrower than the head

• Rasping mouthparts

• Feeds on epithelial scales, scabs, feathers and other bodily debris

• Speices occurs on both mammals and birds

Anoplura

Also known as sucking lice

• Narrow head

• Thorax wider than the head

• Powerful legs

• Piercing mouthparts

• Feed on blood and tissue fluids

• Heavy infestations can cause anaemia

• Species occur only on mammals

Life Cycle

• The whole life cycle takes 2-3 weeks

• The lice spends its whole life on the animal
  • But, can survive for one week off the animal

• In some species parthenogenesis can occur

• Close contact transmission can occur

1. Eggs

• Known as nits

• Cemented to hairs

2. Nymphs

• Nymphs hatch from the egg (no larval stage)

• Undergoes several moults

3. Adults

• Females can lay up to 10 eggs per day

Control

• Few insecticides will kill lice eggs on the animal

• Two treatments are needed to kill nymphs emerging from eggs at the time of the initial treatment and those that will emerge 2-3 weeks later
  • At two week intervals
  • Or a product with a two week residual activity can be used

Anopleura lice are more susceptible to systemic insecticide treatment than mallophaga lice

• Resistance to insecticides may become a problem so alternating the chemicals used and avoiding pour on treatments (which have a greater risk of resistance developing) should be considered